dicom.Writer and dicomio.Writer

[cajund]

HI there, this is more of a question than and issue, but I wanted to explain an issue I encountered with the various go-netdicom repos out there (see: #246)

When interacting with a network connection data PDU's (actions DT-1 and AR-7) it's necessary to encode a DIMSE message using what appears to be an equivalent to your dicomio.Writer. (before refactor, is was dicomio.Encoder.). In the original version "WriteElement" was an exposed function from the dicom object, not presented as function receiver. So, it was callable by passing in a dicomio.Encoder. Here's the line:

https://github.com/grailbio/go-dicom/blob/b0e216a1c5cd39a087b0b20538327cc4ae16abdd/writer.go#L117

Here's my challenge, in your dicom.NewWriter() function, you are creating a new dicomio.Writer.

dicom/write.go

Line 40 in 4c45b44

func NewWriter(out io.Writer, opts ...WriteOption) (*Writer, error) {

However, in my situation, I need to pass in an already created dicomio.Writer (or at least an io.Writer) created in previous steps in this process. Would you have any suggestions here, or should I simply update dicomio with a function that returns the embedded io.writer?

Thanks for your help and great work.

[cajund]

Here's an example presenting the challenge:

New function in dicomio to return the embedded io.Writer:

func (w *Writer) ReturnWriter() io.Writer {
	return w.out
}

And the implementation, note the back and forth between the two objects. I also need to continue testing to make sure the same io.Writer is present throughout. Since I am working on merging a lot of code, I am likely way off base here...

func EncodeMessage(e *dicomio.Writer, v Message) error {

	b := &bytes.Buffer{}
	subEncoder := dicomio.NewWriter(b, binary.LittleEndian, true)
	if err := v.Encode(subEncoder); err != nil {
		return fmt.Errorf("EncodeMessage: error encoding message: %w", err)
	}

	// DIMSE messages are always encoded Implicit+LE. See P3.7 6.3.1.
	e.SetTransferSyntax(binary.LittleEndian, true)

	dicomWriter, err := dicom.NewWriter(e.ReturnWriter())
	if err != nil {
		return fmt.Errorf("EncodeElements: Unable to create writer: %s", err)
	}
	elem, err := NewElement(tag.CommandGroupLength, uint32(b.Len()))
	if err != nil {
		return fmt.Errorf("EncodeMessage: failed to write element: %w", err)
	}
	if err := dicomWriter.WriteElement(elem); err != nil {
		return fmt.Errorf("EncodeMessage: error writing element: %w", err)
	}
	if err := e.WriteBytes(b.Bytes()); err != nil {
		return fmt.Errorf("EncodeMessage: error writing bytes: %w", err)
	}

	return nil
}

Seems like this should be cleaner, but welcome any thoughts on the matter.

Thanks,